Problem: Solve for $x$ and $y$ using substitution. ${-6x-6y = 12}$ ${y = -4x-11}$
Answer: Since $y$ has already been solved for, substitute $-4x-11$ for $y$ in the first equation. ${-6x - 6}{(-4x-11)}{= 12}$ Simplify and solve for $x$ $-6x+24x + 66 = 12$ $18x+66 = 12$ $18x+66{-66} = 12{-66}$ $18x = -54$ $\dfrac{18x}{{18}} = \dfrac{-54}{{18}}$ ${x = -3}$ Now that you know ${x = -3}$ , plug it back into $\thinspace {y = -4x-11}\thinspace$ to find $y$ ${y = -4}{(-3)}{ - 11}$ $y = 12 - 11$ $y = 1$ You can also plug ${x = -3}$ into $\thinspace {-6x-6y = 12}\thinspace$ and get the same answer for $y$ : ${-6}{(-3)}{ - 6y = 12}$ ${y = 1}$